1. Field of the Invention
The invention relates to the area of pressure monitoring devices for blood lines.
2. Description of the Related Art
In an extra-corporeal blood treatment blood is extracted from a patient, circulated in an extra-corporeal blood circuit that comprises a blood treatment unit, and infused back to the patient. Examples for such blood treatments are procedures to be used in case of kidney failure like hemodialysis, hemofiltration or hemodiafiltration. For other organ failures or diseases examples for blood treatments comprise blood oxygenation, blood component separation by centrifuge or filter techniques, or the removal of blood components by adsorption.
During the blood treatment blood is continuously or quasi-continuously circulated in the blood lines of the extra-corporeal blood circuit. In order to monitor the conditions in the extra-corporeal blood circuit the pressure in the arterial blood line leading from the patient to the blood treatment unit and in the venous blood line leading from the blood treatment unit to the patient are continuously measured. In contemporary devices this is accomplished by pressure transducer lines branching off the arterial and the venous lines, respectively, and leading to pressure transducers that are part of the blood treatment device.
To avoid any contamination of the pressure transducers and thus the blood treatment device a first pressure transducer protector filter is used that is dividing the pressure transducer line into a blood line section between the blood line and the filter and a pressure transducer section between the filter and the pressure transducer. Such a contamination is not desirable in view of a possible cross-contamination of the blood of a patient that is treated later with the same device. In addition, the spilled blood may damage the pressure sensor itself and the corresponding electronic circuits.
The pressure transducer protector filter is permeable by a gas like air but not by a liquid like blood. For this purpose preferably hydrophobic filter materials are used. Furthermore, the membrane element in the filter has pores small enough to block the transfer of matter like bacteria and germs that may compromise the sterile hygienic conditions in either side of the filter whenever air passes the filter.
The pressure transducer section is usually separable by connector means comprising a connector and a mating connector. It is thus possible to exchange and dispose the blood lines of the extra-corporeal circuit and the part of the pressure transducer line comprising the blood line section, the first pressure transducer protector filter and the pressure transducer section extending from the filter to the connector means after a blood treatment. These parts may be manufactured as a single piece blood line set. The remaining part of the pressure transducer line and the pressure transducer itself are part of the blood treatment device and are re-used for the next patient. As the first pressure transducer protector filter protects these parts from any blood contact there is no need to exchange them after proper use.
At the start of a treatment a new blood line set is mounted on the blood treatment device and the pressure transducer lines of the blood line set are connected with the help of the connector means to the blood treatment device. When the extra-corporeal blood circuit is primed with a priming solution before a patient is connected, a certain amount of air is trapped in the pressure transducer lines. The air nevertheless transmits the pressure from the corresponding blood line to the pressure transducer. When the pressure rises the air volume will be compressed, but the geometry of the lines is designed so that under normal conditions the blood level will not reach the first pressure transducer protector filter as otherwise the danger arises that the filter is blocked by the blood and that the pressure can no longer be properly transmitted though the filter.
As long as the integrity of the first filter is not damaged the blood cannot enter the pressure transducer section of the pressure transducer line and any contamination is avoided. As all parts of the blood line set that get into contact with the blood are replaced with new and sterile ones before the next patient is treated, cross-contamination cannot occur. The situation is however different should the first pressure transducer protector filter have a rupture. In this case blood can leak through the ruptured filter into the pressure transducer section. Contemporary hemodialysis devices therefore have a second pressure transducer protector filter in the pressure transducer section. The second filter is arranged inside the housing of the hemodialysis device and divides the pressure transducer section in a first part between the two filters and a second part between the second filter and the pressure transducer. This second filter is not part of the disposable blood line set and serves for redundancy purposes only. Should a blood leak occur in the first pressure transducer protector filter, the second pressure transducer protector filter still avoids any contamination and/or damage of the parts behind the second filter, in particular of the pressure transducer.
This prior art arrangement has the disadvantage that a rupture of the first filter is not necessarily noticed by the user of the blood treatment device. Any blood that passed the first filter may have contaminated any part of the first part of the pressure transducer section. In addition the membrane element of the second pressure transducer protector filter may have been at least partially blocked by the leaked blood. Though the pressure transducer is still protected by the second filter, this filter may no longer properly transmit the air pressure. Last not least, if not noticed by a user, the blood remaining in the first part of the pressure transducer section is not removed by exchanging the disposable blood line set, thus giving rise to a possible hygienic problem.